Lymphocyte in vitro cytotoxicity: characterization of mouse lymphotoxin

The flip side of immune surveillance: immune dependency

The growths of many and perhaps all tumors may be stimulated rather than inhibited by a quantitatively low level of immunity. The reason tumors have antigens may be that tumors do not develop in vivo in the absence of at least a minimal immune reaction; in this sense, cancer may be considered an autoimmune disease. This review, based largely on the work of our own laboratory, outlines the data showing that the titration of anti-tumor immunity exhibits the phenomenon of hormesis, i.e. the dose-response curve is non-linear such that low levels of immunity are generally stimulatory but larger quantities of the same immune reactants may inhibit tumor growth. Evidence is also reviewed that suggests that the immune response may vary qualitatively and quantitatively during progression, such that there seems to be, during oncogenesis, a very low level of immune reaction that aids initial tumor growth, followed by a larger reaction that may cause remission of early neoplasms, followed, if the neoplasm survives, by a relative immunologic tolerance to the tumor that may be dependent, at least in part, on suppressor cells. This knowledge may help to explain some clinical observations concerning the relationships among tumor types and the organ distribution of metastases.

Direct cytolysis by partially-purified preparations of immune interferon

Mouse IFN gamma preparations purified 30-fold were found to have direct cytolytic activity against a number of tumor and normal cells. Cell killing was determined using a sensitive, rapid and accurate assay which employed very low numbers of cells and very small quantities of interferon. The cytolytic activity of IFN gamma on 11 murine tumor cell lines was investigated. A 20-fold difference was found between the most-sensitive cell type, P-388 lymphoma, versus the most resistant cell type, C127v leukemia. A number of normal mouse cells was also found to have low to intermediate sensitivity to the cytolytic action of IFN gamma. Human IFN gamma was also shown to have cytolytic activity which, like mouse IFN gamma, was relatively species-specific. Direct cytolysis was not found to be a characteristic of IFN-alpha/beta. Different mechanisms of action for the antiviral and cytolytic activities of IFN gamma are indicated because the cytolytic titer of IFN gamma did not parallel its antiviral titer on most cell types and increasing the cell number produced a decrease in the cytolytic titer and an increase in the anti-viral titer. High concentrations of IFN gamma (i.e., 2,900 units/ml) resulted in complete lysis of cells within 24 h, while lower concentrations (i.e., 700 units/ml) resulted in a reversible inhibition of cell growth during this time period. Evidence that the cytolytic substance in the IFN gamma preparation was IFN gamma include the following: (1) both antiviral and anticellular activities copurified through a 30-fold purification; and both activities were (2) relatively species-specific; (3) sensitive to heat; (4) inactivated by low pH and (5) neutralized by antibodies to IFN gamma. Therefore, we propose the possibility that direct cytolysis is yet another of IFN gamma's distinctive antivities.

Species specificity of guinea pig and human lymphotoxin colony inhibitory activity

The species specificity of lymphotoxin colony inhibitory activity was measured by in vitro colony growth of neoplastic and nonneoplastic cells in the presence of lymphotoxin from the same or from a xenogeneic species. Growth of guinea pig, rat, and mouse neoplastically transformed cells was inhibited by guinea pig lymphotoxin. Colony formation of benzo(a)pyrene transformed 104C1 guinea pig cells was inhibited 45% with lymphotoxin at 42 units/ml medium; nontransformed 104 and 118 guinea pigs cell were not inhibited. Alpha L929, a spontaneously transformed mouse cell, was completely inhibited. Dimethylbenz(a)anthracene (DMBA) 3T3-D and R4-2 mouse transformed cells were inhibited 40 and 100%, respectively, but parental nontransformed 3T3 cells were not inhibited. DMBA transformed R-2 and R-6 rat cells were inhibited 20 and 40%, respectively, but secondary nontransformed fetal rat cells were unaffected. In contrast, normal human xeroderma pigmentosum, Lesch-Nyhan and 1220 fibroblast cells were inhibited 50-60%. No inhibition of HeLa or RPMI 2650 human tumor cells occurred. HeLa and RPMI 2650 cells, however, were inhibited 30 and 60%, respectively, by human lymphotoxin, but normal human and tumorigenic guinea pig cells were unaffected. Thus, guinea pig and human lymphotoxin exhibit species specific and differential cytotoxicity mechanisms for normal and tumor cells.

Interferon and cytotoxic factor (cytotoxin) released in the blood of mice infected with Mycobacterium bovis BCG. I. Enhanced production of interferon and appearance of cytotoxin stimulated by capsular polysaccharide of Klebsiella pneumoniae or bacterial lipopolysaccharide

Interferon production stimulated by the active substance (neutral fraction) of the capsular polysaccharide of Klebsiella pneumoniae (neutral CPS-K) in BCG-infected mice was compared with that by bacterial lipopolysaccharide (LPS). Prior infection with BCG increased the responsiveness of mice to the lethal effect of neutral CPS-K as well as to that of LPS. Associated with this, BCG-infected mice showed a markedly enhanced ability to produce interferon after stimulation not only by LPS but also by neutral CPS-K. In addition, a cytotoxic factor (cytotoxin) was found to be released in the serum of BCG-infected mice after injection of these inducers. The kinetics of production of interferon and cytotoxin stimulated by neutral CPS-K were very similar to those stimulated by LPS. The time pattern of cytotoxin production was not in parallel with that of interferon production. Interferon reached a peak 2 hr and cytotoxin 3 hr after injection with these inducers. Interferon and cytotoxin produced by neutral CPS-K showed essentially the same stabilities to heating at 56 C and to treatment at pH 2 respectively as those produced by LPS. Interferon was inactivated by heating at 56 C more rapidly than cytotoxin. Cytotoxin was inactivated by treatment at pH 2 for 24 hr, whereas interferon activity was well preserved after this treatment. These results suggest that both activities are the result of different substances.

Studies on production of biologically active substance which inhibits the intracellular multiplication of Toxoplasma within mouse macrophages

In vitro assessments were carried out to study some biological aspects of immune lymphocytes producing a new lymphokine, called by the authors Toxoplasma growth inhibitory factor (Toxo-GIF), which inhibits the intracellular multiplication of Toxoplasma gondii within nonimmune mouse macrophages. Concanavalin A and phytohemagglutinin-P were found to induce vigorous production of Toxo-GIF, whereas bacterial lipopolysaccharide did not. In vitro treatment of splenic lymphocytes with rabbit anti-mouse thymocyte serum plus complement abolished almost completely their ability to produce Toxo-GIF. Treatment of splenic lymphocytes with inhibitors of protein synthesis, cycloheximide or puromycin resulted in a remarkable reduction of the ability of sensitized lymphocytes to produce this lymphokine. Thus the production of Toxo-GIF seems to be dependent on the cellular metabolic events of sensitized T-lymphocytes. The significant activity of Toxo-GIF was demonstrable even in the supernate of lymphocyte cultures incubated in serum-free medium and was also evident after immune lymphocytes and homologous antigen were incubated for the relatively short period of 10 h.

Defective PGE reactivity in leucocytes of multiple sclerosis patients

Leucocyte migration inhibition in vitro, in response to antigen or mitogen, is suppressed by PGE2 (0.01-1.0 mug/ml). The susceptibility of leucocytes to such inhibition by PGE2 has been compared using cell preparations obtained from normal individuals, multiple sclerosis patients and from patients with other neurological diseases. The results indicate defective reactivity of leucocytes from multiple sclerosis patients.

Leukocyte mediated cytotoxicity of chemically induced rat salivary gland neoplasms

Chemically induced tumors of the rat submaxillary glands were tested for the presence of tumor antigens by in vitro leukocyte mediated cytotoxicity assays. Since it has been reported that the saliva of humans with oral cancer contains markedly elevated levels of secretory antibody, the rats' saliva specimens were also tested for blocking and/or potentiating "antibody" activity. The results indicate that saliva from tumor-bearing animals potentiated tumor cell killing if either the tumor cells or leukocytes were pretreated. The effect was much more marked when tumor cells were pretreated. Furthermore, the addition of saliva to tumor cells imparted an immunologic cross reactivity which was not present with untreated tumor cells. Control saliva occasionally produced a similar effect, but not as consistently or with the potency of saliva from tumor-bearing animals. Heat inactivation did not abrogate this potentiation. It is inferred that this may indicate a new system of immunologic surveillance, i.e. arming or potentiation of leukocytes by soluble tumor antigens in glandular secretions.

The immune reaction as a stimulator of tumor growth

Various numbers of spleen cells from specifically immunized mice were mixed with constant numbers of target tumor cells, and were inoculated subcutaneously into thymectomized, x-irradiated recipients. Small numbers of admixed immune spleen cells produced a statistically significant, and reproducible, acceleration of tumor growth in the inoculum as compared with controls of either nonimmune spleen cells or spleen cells from animals immune to a different, non-cross-reacting, tumor. Larger. numbers of specifically immune spleen cells, however, produced inhibition of tumor growth. These data imply that the normal immune reaction may have a dual function in relation to neoplasia: (i) stimulation of tumor growth, early in the course of the disease, or whenever the immune reaction is minimal; (ii) inhibition of tumor growth at other times.

Production of macrophage migration inhibition factor by continuous cell lines

Macrophage migration inhibitory factor (MIF) was found in media of human and mouse lymphocyte and fibroblast cell lines that were continuously growing. Its release was dependent on activation of the cells to enter the mitotic cycle, particularly on cells in S phase. The greatest quantity of MIF was detected in supernatants of lymphocytes collected during S phase after the cells were synchronized in G(1) and in supernatants of growing fibroblasts. When the latter were contact inhibited little or no MIF was found in media. MIF was also released into media of cells proliferating in homologous serum in the absence of fetal calf serum and into media lacking any protein. The MIF produced by lymphocyte lines eluted from Sephadex G-100 in the same fashion as MIF produced by the interaction of sensitized guinea pig cells and antigen. The results indicated that MIF is not a specific mediator of delayed hypersensitivity and cellular immunity and that MIF released by sensitized lymphocytes incubated with antigen merely reflects that fraction of cells activated by antigen to enter the mitotic cycle.